Examples of automobile wheels include a so-called two-piece type in which a generally cylindrical wheel rim and a generally disc-like wheel disc are fitted and welded to each other. A known example of the wheel rim forming such a two-piece automobile wheel includes surface-side and back-side bead seats that support beads of a tire, surface-side and back-side flanges, and a well provided between the surface-side and back-side bead seats and dented inward. A known example of the wheel disc includes a circular hub mounting portion that is to be coupled to a hub of an axle, a plurality of spokes provided to extend radially outward from the outer peripheral edge of the hub mounting portion, and an annular disc flange formed continuously with the outer ends of the spokes. The wheel disc is formed with a plurality of ornamental holes defined between adjacent spokes by the spokes and the disc flange. The disc flange of the wheel disc is fitted inside the well of the wheel rim, and the wheel disc and the wheel rim are welded to each other to form an automobile wheel.
An example of the automobile wheel is proposed in Published Japanese Translation of PCT Application No. 2009-525191 (see paragraphs [0016] to [0019] and FIGS. 1 and 2) discussed above, for example, in which a wheel disc includes a flat cylindrical disc flange formed to extend substantially axially and in which ornamental holes are defined by the disc flange and adjacent spokes.
In the automobile wheel according to Published Japanese Translation of PCT Application No. 2009-525191 (see paragraphs [0016] to [0019] and FIGS. 1 and 2) discussed above, the disc flange of the wheel disc is formed in a flat cylindrical shape, and is not curved in the surface-side and back-side direction. Therefore, the ornamental holes which extend to the disc flange are formed to be relatively large, which advantageously provides an excellent design quality. When an automobile to which the automobile wheel is attached is running, the disc flange of the wheel disc receives a radial load via the wheel rim, and a bending load and a torsional load via the spokes from the hub mounting portion. Since the disc flange according to Published Japanese Translation of PCT Application No. 2009-525191 (see paragraphs [0016] to [0019] and FIGS. 1 and 2) has a flat cylindrical shape, the disc flange may be easily deformed when the above load is applied and tends to cause a stress concentration on a welded portion between the wheel rim and the wheel disc. In addition, it is concerned that the stress concentration may reduce the fatigue life.
In order to address the foregoing issues, the present invention proposes an automobile wheel that can exhibit high strength and rigidity.